1. Field of the Invention
The present invention relates to a throwaway insert which is detachably attached to a throwaway cutting tool (hereinafter referred to as a cutting tool), and the present invention also relates to a cutting tool provided with such a throwaway insert.
2. Background Art
As examples of such a throwaway insert and cutting tool, the inventors of the present invention have proposed a throwaway insert and a rotating cutting tool in Japanese Unexamined Patent Application, First Publication No. 2000-141123. In this case, the throwaway insert comprises a first cutting edge (a major cutting edge) having a predetermined length, and a second cutting edge (a corner cutting edge) which extends radially and outwardly from the first cutting edge as viewed from an axis of rotation, and which has a relatively small radius of curvature, and the throwaway insert is adapted to be detachably attached to a cutting tool main body (rotating cutting tool) in such a manner that the throwaway insert projects from the outer periphery of the cutting tool main body while a predetermined cutting angle is applied to the first cutting edge when being attached to the cutting tool main body. The rotating cutting tool enables continuous formation, in a workpiece to be machined, of a plane portion and a wall connected to the plane portion with a predetermined angle by rotating about the axis of rotation with the above-mentioned throwaway insert while translating the axis of rotation. According to such a throwaway insert and a cutting tool, if compared with a cutting tool provided with a circular disc-shaped throwaway insert, it is possible to improve efficiency of cutting because the contact length between the cutting tool and the workpiece, and therefore, cutting resistance depending on the contact length are not significantly changed between the case in which the plane portion is machined and the case in which the wall is machined, and because the rotating speed of the cutting tool when the plane portion is machined need not be set as low as when the wall is machined.
In such conventional throwaway insert and cutting tool, a side edge, which is connected to the second cutting edge, and which is directed radially and outwardly with respect to the cutting tool, is formed so as to incline radially and inwardly with respect to the axis of rotation in order to avoid interference with the wall to be machined, and as a result, there is formed a gap between an end of the side edge and the outermost point of the throwaway insert, which defines the maximum radius of rotation. In the above-mentioned throwaway insert, because the side edge, which is connected to the second cutting edge, is formed in a straight shape, and because the gap between the side edge and the wall gradually decreases as the distance from the second cutting edge decreases even though the side edge is inclined radially and inwardly, cut chips tend to be packed up in the narrow gap when, in particular, cutting is performed while the axis of rotation is directed in the horizontal direction, and as a result, the machined surface (the wall) may be damaged, or the throwaway insert may be chipped off. Moreover, the above-mentioned throwaway insert is substantially formed in a polygonal plate shape, and the throwaway insert is attached to the cutting tool main body in such a manner that a pair of side edges, which include therebetween a corner that diagonally faces to the second cutting edge, are engaged with support surfaces of the cutting tool main body. Because the engagement is achieved by abutting flat surfaces, it is difficult to ensure sufficient rigidity in fixation of the throwaway insert against changes in the direction of cutting load applied to the throwaway insert between when the plane portion is machined and when the wall is machined, and as a result, the throwaway insert may be undesirably shifted.